Plastic materials today account for between 15 and 20 percent by weight in automobile construction, and the trend is rising. These are frequently exterior and interior parts, wherein the corresponding visual, haptic and functional properties are imparted to the latter by adhesively bonding injection molded components with different surface decors. Rising requirements in regard to quality and cost effectiveness, as well as resource efficiency and global competitive pressure, increase the need to use recycled plastic materials.
Plastic parts may be used in particular as injection molded bodies for the interior of automobiles, such as for example instrument panels, door linings or center consoles. These may be provided with a decor or painted. In many applications in the automotive field, cost pressure and the shortage of petrochemical resources are leading to a greater acceptance of using recycled materials.
When plastic materials are used that contain thermoplastic, thermoset recycled materials that are either fiber-reinforced or not reinforced, or recycled fibers, good binding to the surrounding polymer matrix is needed so that no worsening of the mechanical properties occurs.
Binding of fibers, for example, can occur by way of complex surface treatment and activation of the particular fiber (such as glass fiber, carbon fiber, natural fiber). When recycled materials are used, these can be blended with the polymer and compounded using an extruder, or admixed directly to the pure polymer during the production operation and melted jointly in the injection molding machine, wherein a homogeneous mixture forms.
A challenge can be the poor thermodynamic compatibility of the material components, which may be attributable to the different polarities of the material components.
The trend of admixing an unrecycled plastic material to the recycled plastic materials may have disadvantages. For example, the recycled material may be admixed to the untreated plastic material in a certain proportion directly at the injection molding machine, or is previously compounded.
Polypropylene and reinforced polypropylene are plastic materials that can be inexpensive and may be used for injection molded parts. Due to the non-polar properties of polypropylene, admixing thermoset recycled plastic materials, for example, can be problematic because these generally comprise polar components in the molecule. Binding of the thermoset component to the polymer matrix, such as polypropylene, may be insufficient, causing partial or semi-partial separation to occur. The inadequate binding of the two components manifests can create worsened mechanical properties, such as reduced impact resistance values and notched bar impact values. Impact resistance can define a measure of the ability of the material to absorb shock energy and impact energy without breaking.